An electric vehicle or a hybrid electric vehicle mounts a motor as a power source of the vehicle, and is typically provided with an electric power converter such as an inverter for controlling the electric power supplied to the motor. The electric power converter includes a power module that houses a semiconductor element for electric power such as an insulated gate bipolar transistor (IGBT), a drive circuit that drives the power module, a control circuit that controls the power module and the drive circuit, and a capacitor for smoothing a current. Among them, the capacitor is a part typically has a low heat resistance temperature and is easily affected by heat. In the conventional inverter, since the heating value of a smoothing capacitor is small, that has not been that big of a problem. However, in recent years, there is a tendency that the inverter for vehicle is increased in current capacity and is decreased in size, and therefore, cooling of the smoothing capacitor becomes a problem. As an example of a structure of the capacitor for enhancing the cooling efficiency, Japanese Patent Application Laid-Open No. 2009-289943 discloses a structure to cool the capacitor with cooling water, for example.
In the smoothing capacitor, a member that generates heat is not only the capacitor element, but also an electrode bus bar that may generate large Joule heat. The bus bar is not provided with countermeasures for cooling, and cannot obtain sufficient effect, which becomes an issue.